Ultrasonic Phased Array used to create the standing waves to levitate the objects (https://96ochiai.ws/3DOFacoustic)

Acoustic levitation is not a new phenomenon. The technique uses the principle of standing waves to keep a small object at a fixed point in space by counteracting the force of gravity with acoustic radiation pressure. In standard arrangements, the transducer and reflector create the standing wave parallel to the pull of gravity – i.e. the transducer is usually pointing up. What makes this demo different is the orientation of the wave, and the ability to manipulate the position of the nodes by tuning the array. Since the array works at ultrasonic frequencies, there is no sound produced within the range of human perception. The video below is a very neat demonstration of the technique